1. Field of the Invention
The present invention relates to techniques for performing oilfield operations relating to subterranean formations having reservoirs therein. More particularly, the invention relates to techniques for performing oilfield operations involving an analysis of oilfield production conditions, such as gas-lift configuration, production rates, equipment and other items, and their impact on such operations.
2. Background of the Related Art
Oilfield operations, such as surveying, drilling, wireline testing, completions, production, planning and oilfield analysis, are typically performed to locate and gather valuable downhole fluids. For example, surveys are often performed using acquisition methodologies, such as seismic scanners or surveyors to generate maps of underground formations. These formations are often analyzed to determine the presence of subterranean assets, such as valuable fluids or minerals. This information is used to assess the underground formations and locate the formations containing the desired subterranean assets. This information may also be used to determine whether the formations have characteristics suitable for storing fluids. Data collected from the acquisition methodologies may be evaluated and analyzed to determine whether such valuable items are present, and if they are reasonably accessible.
Similarly, one or more wellsites may be positioned along the underground formations to gather valuable fluids from the subterranean reservoirs. The wellsites are provided with tools capable of locating and removing hydrocarbons such as oil and gas, from the subterranean reservoirs. Drilling tools are typically deployed from the oil and gas rigs and advanced into the earth along a path to locate reservoirs containing the valuable downhole assets. Fluid, such as drilling mud or other drilling fluids, is pumped down the wellbore through the drilling tool and out the drilling bit. The drilling fluid flows through the annulus between the drilling tool and the wellbore and out the surface, carrying away earth loosened during drilling. The drilling fluids return the earth to the surface, and seal the wall of the wellbore to prevent fluid in the surrounding earth from entering the wellbore and causing a “blow out”.
During the drilling operation, the drilling tool may perform downhole measurements to investigate downhole conditions. The drilling tool may also be used to take core samples of subsurface formations. In some cases, the drilling tool is removed and a wireline tool is deployed into the wellbore to perform additional downhole testing, such as logging or sampling. Steel casing may be run into the well to a desired depth and cemented into place along the wellbore wall. Drilling may be continued until the desired total depth is reached.
After the drilling operation is complete, the well may then be prepared for production. Wellbore completions equipment is deployed into the wellbore to complete the well in preparation for the production of fluid therethrough. Fluid is then allowed to flow from downhole reservoirs, into the wellbore and to the surface. Production facilities are positioned at surface locations to collect the hydrocarbons from the wellsite(s). Fluid drawn from the subterranean reservoir(s) passes to the production facilities via transport mechanisms, such as tubing. Various equipments may be positioned about the oilfield to monitor oilfield parameters, to manipulate the oilfield operations and/or to separate and direct fluids from the wells. Surface equipment and completion equipment may also be used to inject fluids into reservoir either for storage or at strategic points to enhance production of the reservoir.
During the oilfield operations, data is typically collected for analysis and/or monitoring of the oilfield operations. Such data may include, for example, subterranean formation, equipment, historical and/or other data. Data concerning the subterranean formation is collected using a variety of sources. Such formation data may be static or dynamic. Static data relates to, for example, formation structure and geological stratigraphy that define the geological structures of the subterranean formation. Dynamic data relates to, for example, fluids flowing through the geologic structures of the subterranean formation over time. Such static and/or dynamic data may be collected to learn more about the formations and the valuable assets contained therein.
Sources used to collect static data may be seismic tools, such as a seismic truck that sends compression waves into the earth. Signals from these waves are processed and interpreted to characterize changes in the anisotropic and/or elastic properties, such as velocity and density, of the geological formation at various depths. This information may be used to generate basic structural maps of the subterranean formation. Other static measurements may be gathered using downhole measurements, such as core sampling and well logging techniques. Core samples may be used to take physical specimens of the formation at various depths. Well logging involves deployment of a downhole tool into the wellbore to collect various downhole measurements, such as density, resistivity, etc., at various depths. Once the well is formed and completed, fluid flows to the surface using production tubing and other completion equipment. As fluid passes to the surface, various dynamic measurements, such as fluid flowrates, pressure, and composition may be monitored. These parameters may be used to determine various characteristics of the subterranean formation.
Techniques have been developed to model the behavior of geological formations, downhole reservoirs, wellbores, surface facilities as well as other portions of the oilfield operation. Examples of these modeling techniques are described in Patent/Application/Publication Nos. U.S. Pat. No. 5,992,519, WO2004/049216, W01999/064896, U.S. Pat. No. 6,313,837, US2003/0216897, U.S. Pat. No. 7,248,259, US2005/0149307, and US2006/0197759. Typically, existing modeling techniques have been used to analyze only specific portions of the oilfield operations. More recently, attempts have been made to use more than one model in analyzing certain oilfield operations. See, for example, Patent/Publication/Application Nos. U.S. Pat. No. 6,980,940, WO2004/049216, US2004/0220846, and U.S. Ser. No. 10/586,283. Additionally, techniques for modeling certain aspects of an oilfield have been developed, such as OPENWORKS™ with, e.g., SEISWORKS™, STRATWORKS™, GEOPROBE™ or ARIES™ by LANDMARK™; VOXELGEO™, GEOLOG™ and STRATIMAGIC™ by PARADIGM™; JEWELSUITE™ by JOA™; RMST™ products by ROXAR™, and PETREL™ by SCHLUMBERGER™.
Techniques have also been developed to enhance the production of oilfield from subterranean formations. One such technique involves the use of gas-lifted wells. Gas lift is an artificial-lift method in which gas is injected into the production tubing to reduce the hydrostatic pressure of the fluid column. The resulting reduction in bottomhole pressure allows the reservoir liquids to enter the wellbore at a higher flowrate. The injection gas is typically conveyed down the tubing-casing annulus and enters the production train through a series of gas lift valves. Various parameters for performing the gas lift operation (i.e., lift configuration), such as gas lift valve position, operating pressures and gas injection rate, may be determined by specific well conditions. The injected gas (or lift gas) is provided to reduce the bottom-hole pressure and allow more oil to flow into the wellbore. While the discussion below refers to lift gas, one skilled in the art will appreciate that any resource (e.g., gas, energy for electrical submersible pump (ESP) lifted well, stimulation agents such as methanol, choke orifice size, etc.) may be used to provide or enhance lift.
There are many factors to consider in designing a gas lift operation. The optimal conditions for performing a gas lift operation may depend on a variety of factors, such as the amount of lift gas to inject, inflow performance, equipment (e.g. tubing), surface hydraulics, operating constraints, cost, handling capacities, compression requirements and the availability of lift gas. Moreover, a gas lift well network (i.e., a network including gathering network and at least one gas lift well) may be constrained by the amount of gas available for injection or at other times the total amount of produced gas permissible during production due to separator constraints. Under either of these constraints, engineers may allocate the lift gas amongst the wells to maximize the oil production rate. This is an example of a real world scenario that can be modeled in network simulators.
Techniques have also been developed to predict and/or plan production operations, such as the gas lift operation. For example, a gathering network model may be used to calculate the optimal amount of lift gas to inject into each well based on static boundary conditions at the reservoir and processing facility. Other methods of increasing production in oilfields may include electrical submersible pump (ESP) lifted wells, stimulation by chemical injection, etc. Examples of some gas lift techniques are shown in Patent/Publication/Application Nos. US2006/0076140 and US2007/0246222. Additionally, techniques for modeling certain aspects of an oilfield have been developed, such as PIPESIM™ and GOAL™ by SCHLUMBERGER™ and published in a Society of Petroleum Engineers paper entitled “A Gas Lift Optimization and Allocation Model for Manifold Subsea Wells,” SPE20979 by R. Edwards et al.
Despite the development and advancement of reservoir simulation techniques in oilfield operations, a need exists to provide techniques capable of modeling and implementing lift gas operations based on a complex analysis of a wide variety of parameters affecting oilfield operations.